Download Determinants of GFR - BHS116.3 Physiology III

Determinants of GFR
• GFR = Capillary filtration coefficient X Net
filtration pressure.
• Increased glomerular Capillary filtration
coefficient increases GFR.
– Probably not a primary mechanism for day-to-day
regulation of GFR.
– Glomerular Capillary filtration coefficient is
changed in some disease states such as
diabetes millitus.
Determinants of GFR
• GFR = Capillary filtration coefficient X Net
filtration pressure.
• Increased hydrostatic pressure in Bowman’s
capsule decreases GFR (inverse is also true).
– Normally, not a primary mechanism for day-to-day
regulation of GFR.
– Hydrostatic pressure in Bowman’s capsule can change
in some pathologic conditions such as obstruction of the
urinary tract.
Guyton’s Textbook of Medical Physiology 26-12
Determinants of GFR
• GFR = Capillary filtration coefficient X Net
filtration pressure.
• Increased glomerular capillary colloid osmotic
pressure decreases GFR.
– Two factors regulate glomerular capillary colloid osmotic
pressure:
• Arterial plasma colloid osmotic pressure.
• Filtration fraction.
Guyton’s Textbook of Medical Physiology 26-12 & 13
Determinants of GFR
• Increased glomerular capillary colloid osmotic
pressure decreases GFR (cont.)
– Filtration fraction = GFR/renal blood flow
– Such that, a lower rate of blood flow into the
glomerulus causes an increase in the filtration
fraction
• decreased plasma volume with constant filtration
volume increasing the protein concentration.
• results in an increase in Glomerular colloid osmotic
pressure which tends to decrease GFR.
– inverse is also true.
Determinants of GFR
• GFR = Capillary filtration coefficient X Net
filtration pressure.
• Increased glomerular capillary hydrostatic pressure
increases GFR.
– Three variables determine the glomerular hydrostatic
pressure.
• Arterial pressure.
• Afferent arterial resistance.
• Efferent arterial resistance.
Guyton’s Textbook of Medical Physiology 26-12
Determinants of GFR
• Increased arterial pressure increases
glomerular capillary hydrostatic pressure
resulting in increased GFR.
Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed
Determinants of GFR
• Increased afferent arterial resistance decreases
blood flow to the glomerular capillary resulting in
decreased glomerular capillary hydrostatic
pressure and reduced GFR.
Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed
Determinants of GFR
• Decreased afferent arterial resistance
(dilation) _increases_ glomerular capillary
hydrostatic pressure and GFR.
Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed
Determinants of GFR
• Moderate increases in efferent arterial
resistance (constriction) increase glomerular
capillary hydrostatic pressure and slightly
increases GFR.
Guyton’s Textbook of Medical Physiology 26-12
Determinants of GFR
• A severe increase in efferent arterial resistance
(constriction) increases glomerular capillary
hydrostatic pressure, but also increases the colloid
osmotic pressure (due to the decreased renal blood
flow). This results in a net decrease in GFR.
Guyton’s Textbook of Medical Physiology 26-14
Renal blood flow
• The Kidneys get ~22% of the cardiac output.
– Greater than what is needed to supply kidneys
with nutrients and remove waste products.
– Great volume is necessary to supply enough
plasma for high GFRs.
– The renal cortex receives most of the blood.
– The renal medulla receives only 1-2% of the
blood.
• Renal blood flow is determined by the
pressure gradient across the renal
vasculature divided by the total renal vascular
resistance.